More and more electronic equipment is portable and requires wireless power supplies for the comfort of the user. Thus, batteries or rechargeable accumulators, in the following called batteries for simplicity, are applied to power the equipment. To fulfill the demand for high output, i.e. high audio volume when active, the product should be energy efficient at the same time.
The idle loss in an audio amplifier is related to the amplifiers rail-voltage (supply voltage). To minimize this idle loss, it is generally known for amplifier systems to regulate the output rail-voltage from the amplifiers power supply. An adaptive rail-voltage regulation is enabled for analyzing the rail-voltage requirement based on the level of the audio signal, typically the amplitude level; thus, it is possible to adjust the rail-voltage high enough to avoid voltage clipping but not considerably higher than necessary, so that idle loss is minimized.
US patent application No. 2010/0164630 by Witmer et al. discloses a method reducing the average power consumption for an amplifier. A digital audio input signal is split into two parts, of which one is delayed before being fed into an amplifier for output to the loudspeaker, and the other signal is processed for determining signal amplitude information, which is used to adjust the maximum available supply current for the amplifier of least sufficient magnitude to avoid distortion of the delayed signal.
US patent application No 2009/0220110 by Bazarjani et al. discloses a system and method for power consumption for audio playback, where a signal envelop is evaluated for regulating the power for the amplifier.
European patent application No. EP1317105 by Melsa, assigned to Texas Instruments Inc. discloses a line driver using a class G amplifier and programmable peak detector. The peak detector analyzes the digital input signal which is used for adjustment of the rail voltage of the amplifier. Other amplifier systems are disclosed in European patent application EP2432120, U.S. Pat. No. 5,396,194 by Williamsen, US patent application No. 2003/0080816, and International patent application WO2009/019459.